The air was then being redirected to New Zealand with strong westerlies, he said.
"It just gets caught up in the roaring forties and comes straight over us. The result of that is kind of like a leaf-blower against a hose, because the southerly is trying to come up to us, but is being cut off at the knees by the westerlies."
It was a different picture from the near- or below-average temperatures of last year's winter.
"Because we are two small, mountainous islands in the roaring forties, our weather every year is quite different, but the main difference [this year] is that we are not really getting the big southerlies."
How long will it last?
"I think this is what we will be seeing between now and, let's say the second week of August.
"It doesn't mean that we can't have brutally cold southerlies coming in August and September, but it does limit how cold it can really be across the country."
Between July and September, the National Institute of Water and Atmospheric Research (Niwa) predicted that temperatures had a 60 to 70 per cent chance of being above average in all regions, although it said that frosts and cold snaps would occur from time to time.
Seasonal rainfall was also about equally likely to be near normal or above normal for all regions.
Today's outlook
Auckland: Showers and strong southwesterlies, gales gusting to 90km/h. High: 15C
Whangarei: Fine breaks with the odd shower, strong southwesterlies. 17C
Hamilton: Few showers, fine breaks. Strong southwesterlies. 15C
Tauranga: Morning showers, strong southwesterlies. 16C
Wellington: Fine day, evening northwesterly. 13C